Spinal fixation systems may be used in surgery to align, adjust and/or fix portions of the spinal column, i.e., vertebrae, in a desired spatial relationship relative to each other. Many spinal fixation systems employ a spinal fixation element, e.g. a spinal fixation rod, for supporting the spine and for properly positioning components of the spine for various treatment purposes. Vertebral bone anchors, comprising pins, bolts, screws, and hooks, engage the vertebrae and connect the supporting spinal fixation element to different vertebrae. The size, length and shape of the spinal fixation element depend on the size, number and position of the vertebrae to be held in a desired spatial relationship relative to each other by the apparatus.
Spinal fixation elements can be anchored to specific portions of the vertebra. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra, and a head portion having a spinal fixation element-receiving portion for receiving a spinal fixation element. A set-screw, plug, cap or similar type of closure mechanism is used to lock the spinal fixation element into the spinal fixation element-receiving portion of the pedicle screw.
In conventional spinal surgery, first, anchoring devices are attached to vertebra, then a spinal rod is aligned with the anchoring devices and secured. For example, for conventional pedicle screw assemblies, first the engagement portion of each pedicle screw is threaded into a vertebra. Once the pedicle screw assembly is properly positioned, a spinal fixation rod is seated in the rod-receiving portion of each pedicle screw head. The rod is locked into place by tightening a cap or similar type of closure mechanism to securely interconnect each pedicle screw to the fixation rod. This type of conventional spinal surgical technique usually involves making a surgical access opening in the back of the patient. Because exact placement of the screw assemblies depends on a patient's particular bone structure and bone quality, the exact position of all screw assemblies cannot be known until after all the assemblies are positioned. Adjustments, such as bending, are made to the spinal rod to ensure that it aligns with each screw assembly.
When placing the spinal fixation element in a long construct, the spinal fixation element may be inserted in an inverted orientation to facilitate insertion and positioning of the spinal fixation element below fascia. Consequently, the spinal fixation element needs to be rotated prior to final positioning in order to match the curvature of the spine. The contemporary medical devices, such as spinal fixation element holders, do not accommodate the rotation of the spinal fixation element while performing a minimally invasive procedure. Rotating the spinal fixation element percutaneously typically requires an additional skin incision or increasing the size of the existing skin incision. Additionally, it is desirable to make minimal rotary adjustments for better control. Currently, surgeons have to select a long rod to provide a holding surface when the rod is placed through the skin incision. The extra portion of the rod is cut in situ, extending the surgery time and posing the risk of cutting the rod at an unintentional location.
The contemporary medical devices also require re-engagement of the device to the spinal fixation element multiple times and often a second instrument is required during the re-engagement to prevent the spinal fixation element from slipping back toward the initial position. Therefore, there is a need for an instrument that will accommodate the rotation of a spinal fixation element while preventing the spinal fixation element from rotating back toward the initial position following adjustment during a minimally invasive procedure.